A computer-implemented method technique can intercept, at a server including one or more processors, a first request for a source document representing a web page, the first request being transmitted from a computing device to a web server. The first request can include web browser information indicating web browser software executing on the computing device. The technique can intercept the source document being transmitted from the web server to the computing device in response to the first request. The source document can specify one or more fonts in which to display text in the source document. The technique can generate the web page, determine unique characters displayed at the web page, and obtain one or more font subsets. The technique can then transmit information to the computing device based on whether the web browser software is capable of displaying a font family having a plurality of fonts.